He is now leading calls to legalise cannabis for medical use. He wants to make the drug available to patients like him who suffer agonising pain 24 hours a day.

Callum, 28, also shattered his pelvis in the huge explosion after he stepped on a boobytrap bomb while on patrol in Helmand five years ago.

Callum Brown with Laura

Speaking to the Daily Record, he said: “As well as my other injuries, I have no skin on my backside – it’s just thin scar tissue so the nerve damage and the phantom pains are the main reason for smoking.

“It also helps with depression as it’s easy to get a bit down. After seeing kids suffering and mothers of dead children screaming in my face in Afghanistan, asking why we did this, I decided enough was enough.

“I wanted to speak out to make sure children don’t go on suffering.

“Kids with epilepsy and other conditions can be helped with some of the active ingredients in cannabis.

“Cannabis has been used for thousands of years. Ancient people knew all about its medicinal qualities.

“I shouldn’t have to be a criminal to get something that eases my pain and makes life easier."

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He added: “After I was injured in Afghanistan, the doctors had me on strong painkillers.

“These chemicals had very strong side-effects – they could even make you suicidal, which obviously wasn’t good when I was trying to cope with my injuries.

“With cannabis, there is no down side. It eases my pain.

“My injuries mean I am effectively sitting on the base of my spine all day. When I am sitting down, I am sitting on bone. Cannabis takes the edge off the searing pain.

“It should be legal for medical use for people like me who really need it, not people who just take it to get high.

“Cannabis has all sorts of medical uses – I saw some terrible suffering in Afghanistan, especially with young kids.

“I just want to make sure children get whatever they need. I don’t want suffering children to be denied anything that could help take away their pain.

“It’s important that doctors have the full arsenal of pain relief available to them. I have seen enough suffering and don’t want to witness any more.

“As I get older, I realise how important it is that we look out for people, especially young ones. In Afghanistan, that was the worst thing, seeing how the kids suffered through no fault of their own.”

Callum Brown and wife Laura

Callum, from Penicuik, Midlothian, is now leading calls for the law to be changed so that British doctors can prescribe the medical cannabis he needs to ease his pain.

Callum, who served with 2 Scots, the Royal Highland Fusiliers, lost two thirds of his body weight as he recovered from the bomb blast in 2011.

At one point, he was taking more than 30 pills a day to deal with the pain – but now he says smoking a small amount of cannabis helps him.

He said: “My mum and wife were there when I woke up. I said, ‘My legs are gone, aren’t they?’ and they just said, ‘Yes’.

“When I was blown up, I was blasted about 30ft into the air. It didn’t even knock me out, I was conscious the whole time. It was amazingly horrible.

“I had even said before I left camp that day that I had a bad feeling about this one.

“I’d offered to take somebody’s place on a foot patrol to give them a rest because it was my last day before my R&amp;R.